Big Six energy provider Scottish Power has been banned from proactive sales for 12 days after failing to meet customer service targets set by Ofgem.

The Spanish-owned firm signed up to the targets in November after the regulator identified customers experiencing long call waiting times and late bills, and that it was not implementing decisions by the industry ombudsman.

It was given three months to meet the commitments and has achieved those relating to call waiting times - which have fallen to less than two minutes - and late bills - down from 75,000 to less than 25,000 - but failed on resolving ombudsman rulings.

Sarah Harrison, Ofgem’s senior partner for enforcement, said: “A sales ban illustrates the difficulties Scottish Power is having delivering the levels of service customers deserve.

“While Ofgem’s targets have driven significant improvements on Scottish Power’s performance, we remain very concerned about how customers are being treated.”

Scottish Power had been ordered to remove its backlog for acting on ombudsman decisions for individual complaints by the end of November.

Ofgem said it had been told by the firm that this target was met in December and that this was confirmed by the ombudsman.

But in January the regulator said it “uncovered new evidence that showed the company had not fully met its November target”. The ombudsman has now found that Scottish Power fell short of the target by 30.